A power mechanism which incorporates a motor therein has been positively used in various vehicles, equipment and the like. Particularly, with respect to a power mechanism used in an applied product such as an electric vehicle such as a wheelchair, an electric stand-on two-wheeled vehicle (for example, Segway (registered trademark)) or the like, a nursing care robot or an electric reel for fishing, there has been a demand for a power mechanism which is small-sized and light-weighted but can output a high torque.
As a method for enabling a power mechanism to output a high torque, a method which uses a reduction gear is named as one example. In this method, a reduction gear which has a plurality of gears is connected to an output shaft (shaft) of a motor so that rotational speed produced by the motor is reduced whereby power whose torque is increased is transmitted from an output shaft of the reduction gear. However, this method additionally requires the reduction gear besides the motor and hence, the number of parts is increased whereby it is difficult to make the whole power mechanism small-sized and light-weighted. Further, problems such as an energy loss in the reduction gear or the generation of noises also newly arise more or less.
As another method, there has been known a direct driving method where a power mechanism is driven only by a motor without using a reduction gear. In this case, it is necessary to increase a torque which can be outputted to some extent.
As a motor which can output a relatively high torque, conventionally, there has been known a motor which uses salient poles (iron cores or cores having a projecting shape) (see patent document 1).
FIG. 16 is a view for describing a conventional motor 900. With respect to coils 950, only the coils which are mounted on salient poles 940 which belong to a first salient pole group 941G and a fourth salient pole group 944G are shown, and the coils mounted on other salient poles are omitted from the drawing. Symbols are not given to a second salient pole group 942G, a third salient pole group 943G, a fifth salient pole group 945G, a sixth salient pole group 946G, a second coil group 952G, a third coil group 953G, a fifth coil group 955G and a sixth coil group 956G.
As shown in FIG. 16, the conventional motor 900 is a motor 900 which includes: a rotor 920 having a permanent magnet 924 where a magnetic pole having an N pole and a magnetic pole having an S pole are alternately arranged along a circumferential direction; and a stator 930 configured such that the stator 930 has a plurality of salient poles 940 on which coils 950 are mounted respectively, the plurality of salient poles 940 are arranged along a circumferential direction, and distal end surfaces of the salient poles 940 opposedly face a surface of the permanent magnet 924 on which the magnetic poles are arranged.
In FIG. 16, the number of salient poles 940 which the stator 930 has is 12.
In the stator 930, the first salient pole group 941G consisting of two salient poles 940, the second salient pole group 942G consisting of two salient poles 940, the third salient pole group 943G consisting of two salient poles 940, the fourth salient pole group 944G consisting of two salient poles 940, the fifth salient pole group 945G consisting of two salient poles 940, and the sixth salient pole group 946G consisting of two salient poles 940 are arranged along a circumferential direction of the stator 930 in this order. Further, the first salient pole group 941G and the fourth salient pole group 944G are arranged so as to be positioned at positions displaced from each other by 180° in terms of a mechanical angle. The second salient pole group 942G and the fifth salient pole group 945G are arranged so as to be positioned at positions displaced from each other by 180° in terms of a mechanical angle. The third salient pole group 943G and the sixth salient pole group 946G are arranged so as to be positioned at positions displaced from each other by 180° in terms of a mechanical angle.
A first coil group 951G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the first salient pole group 941G. A second coil group 952G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the second salient pole group 942G. A third coil group 953G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the third salient pole group 943G. A fourth coil group 954G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the fourth salient pole group 944G. A fifth coil group 955G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the fifth salient pole group 945G. A sixth coil group 956G consisting of two coils 950 connected in series is mounted on two salient poles 940 of the sixth salient pole group 946G.
A U-phase current is supplied to the first coil group 951G and the fourth coil group 954G, a V-phase current is supplied to the second coil group 952G and the fifth coil group 955G, and a W-phase current is supplied to the third coil group 953G and the sixth coil group 956G.
With such a conventional motor 900, the stator (armature) 930 includes the salient poles (core) 940 and hence, it is expected that the motor 900 can acquire a larger output compared to a coreless motor (see a left upper column and the like on page 2 of patent literature 1).